With recent reductions in the size and weight of battery-using equipment, there is a pressing need to reduce the size and weight of batteries and to reduce their thickness. Various types of thin batteries have been proposed for use in such equipment. Among them is a flat battery wherein positive and negative terminals are vertically put together with a separator interposed therebetween and the assembly is sealed in a sheathing film of multilayer construction mainly using a resin film. The sheathing film used therein has a laminate form in which a thin aluminum film is interposed between polyester films and these films are integrated together, and disposed on the innermost side is a heat-sensitive adhesive agent layer in firm form. The upper and lower surfaces of this sheathing film are formed with throughgoing holes, and exposed portions of positive and negative collectors thermally bonded to the inner adhesive layer on the sheathing film are used as positive and negative terminals. Disposed on the positive collector thermally bonded to the sheathing film is a positive active material and disposed on the negative collector is a negative active material, with a separator of polypropylene non-woven fabric interposed therebetween, said separator serving as a liquid retaining material as well. An electrolytic solution, e.g., an inorganic salt, lithium borofluoride, dissolved in .gamma.-butyrolactone, which is an organic solvent, is injected into the separator and positive active material, and then the periphery of the sheathing film is thermally bonded for sealing. This construction in which positive and negative terminals are disposed on both the upper and lower surfaces of the flat battery encounters some problems in the use of the battery. That is, the thinness of the flat battery cannot be effectively utilized when the battery is used. For example, suppose that the flat battery is 1.5 mm thick and that the plate spring-like terminals of the battery receiving case installed on battery-using equipment are 2 mm thick, then the clearance in the interior of the battery receiving case will be required to be at least 5.5 mm, so that the thinness of the flat battery is not effectively utilized. Further, in this case, the flat battery will be located in the middle of the battery receiving case while it is held between the plate spring-like terminals within the battery receiving case, so that the area of contact with the bottom plate of the battery receiving case is reduced, leading to instability and positional deviation. Thus, a construction in which both positive and negative terminals are installed on one surface of the flat battery is advantageous in use. An example of a construction in which both positive and negative terminals are installed on one surface of the flat battery is disclosed in Japanese Laid-Open Utility Model Application No. 91065/1980. With the disclosed construction, however, the battery capacity per unit area cannot be increased because of limitations imposed by the bond portion of the sheathing film and by the withdrawal of the positive and negative terminals. Another construction in which positive and negative terminals are installed on one surface of the flat battery is disclosed in Japanese Laid-Open Patent Application No. 15042/1973, and in this construction the battery itself has terminals on its upper and lower sides, a portion of one terminal being extended to the other, whereby the positive and negative terminals are installed on one surface of the completed flat battery. Thus, structurally, it is necessary to make one terminal portion longer and larger, the construction being complicated.
Thus, there has been desired a battery wherein both positive and negative terminals are installed on either the upper or the lower surface of the flat battery and the battery capacity per unit area can be increased while either the positive or the negative terminal extended inside the sheathing film is small in size and simplified.